Wordpress 1.5 through 2.3.1 uses cookie values based on the MD5 hash of a password MD5 hash, which allows attackers to bypass authentication by obtaining the MD5 hash from the user database, then generating the authentication cookie from that hash.
https://www.redhat.com/archives/fedora-package-announce/2008-January/msg00098.html
https://www.redhat.com/archives/fedora-package-announce/2008-January/msg00079.html
https://exchange.xforce.ibmcloud.com/vulnerabilities/38578
http://www.cl.cam.ac.uk/~sjm217/advisories/wordpress-cookie-auth.txt